The present invention relates to a gas laser.
One known type of gas laser is composed of a capillary tube presenting a capillary passage and made of a nonconductive material, such as glass, ceramics or the like; a reservoir tank in communication with the capillary passage and coaxially enclosing the capillary tube, and having an envelope which is fastened in two axially offset planes to the capillary tube so as to seal the reservoir tank, the tank and tube being filled with an active laser gas; a cathode accommodated in the tank; a counterelectrode in communication with the capillary passage; and mirrors terminating the capillary passage, at least one of the mirrors being partially transparent, or transparent plates oriented at the Brewster angle and cooperating with external mirrors.
A gas laser having the above features is shown in FIG.1 of German Offenlegungsschrift [Laid-open Application] No. 2,343,140. The laser tube illustrated and described there includes a capillary tube of glass provided at one of its ends with an anode which is in communication with the capillary passage provided by the capillary tube. At its other end, the capillary tube has a connection to the reservoir tank which coaxially encloses the capillary tube. The reservoir tank is formed in part by an envelope which is likewise made of glass and contains the cathode of the laser. Both ends of the glass envelope of the reservoir tank are connected to the glass capillary tube.
In such a laser tube, in which both ends of the capillary tube are connected with the envelope of the reservoir tank, there exists the danger, because of the differential heating, and thus differential expansion, of the various parts during laser operation, that the envelope of the reservoir tank will rupture. Moreover, because of the fused connection of the glass envelope to the glass capillary tube at two locations, which is required if the laser is to remain tight for a long period of time even under environmental stresses such as chemical influences, temperature fluctuations and possibly shocks and/or vibrations, this solution suffers from an influence, e.g. widening of the inner diameter of the capillary tube, at two points which has a negative influence on the laser gain. For these reasons, the capillary tubes of lasers are generally fastened only at one side to the envelope of the reservoir tank, as disclosed, for example, in German Offenlegungsschriften Nos. 2,603,267 and 3,003,669. However, this again leads to basic alignment difficulties, particularly in view of the above-mentioned environmental influences.